As is well known in the art, the starting performance of a spark-ignition internal combustion engine tends to be impaired when the engine is operating cold or when the voltage being delivered from the battery forming part of the ignition system of the engine is low.
When the engine is operating cold, the riser portion of the intake manifold of the engine is maintained at a low temperature so that the fuel passed through the riser portion cannot be gasified satisfactorily and is, as a consequence, admitted to the power cylinders of the engine largely in a liquid or emulsified state. For this reason, the gaseous-phase air-to-fuel ratio, viz., the air-to-fuel ratio of the air/fuel mixture which lends itself to combustion in the power cylnders of the engine becomes higher than that of the mixture which is to be produced by the fuel and air actually supplied to the power cylinders. If the gaseous-phase air-to-fuel ratio of the mixture fed to the combustion chambers of the engine is thus higher than air-to-fuel ratios of a combustible range, the mixture fails to be ignited properly and cannot be combusted effectively.
The fuel admitted into each combustion chamber of the engine is gasified in an increasing proportion as the compression stroke of the power cylinder proceeds. The gasifying rate of the fuel in the combustion chamber of the engine notably varies with the velocity of movement of the piston in the power cylinder and accordingly with the output speed of the cranking motor during starting of the engine. If, therefore, the voltage supplied to the cranking motor from the battery of the ignition system of the engine is reduced to a low level so that the cranking motor cannot operate at sufficiently high revolution speeds, the fuel in the combustion chambers of the engine cannot be gasified at satisfactory rates during the compression stroke of the power cylinder. This also results in an increase in the gaseous-phase air-to-fuel ratio of the mixture to contribute to the combustion in the power cylinders and causes improper burning of the mixture in the combustion chambers of the engine.
It is, on the other hand, known to those skilled in the art that the gaseous-phase air-to-fuel mixture in a combustion chamber of a spark-ignition internal combustion engine can be reduced if fuel is supplied to the power cylinder at an increased rate even though the fuel supplied to the combustion chamber is gasified in a limited proportion. This is because an increase in the rate of supply of fuel to a combustion chamber results in an increase in the quantity of the fuel gasified in the combustion chamber. If, therefore, fuel is supplied to the power cylinders of the engine at an increased rate during cranking of the engine, the mixture to contribute to the combustion in the power cylinders will be ignited properly and will accordingly provide an improved cranking performance.
It has therefore been put into practice to suck in fuel into the intake manifold of an internal combustion engine when the choke valve of the engine is in a closed condition during cranking of the engine. Such an expedient is, however, not fully acceptable because the vacuum developed in the intake manifold of the engine is not so high (in absolute value) as to be capable of sucking fuel into the intake manifold at a sufficiently high rate during cranking of the engine when the engine is operating at low speeds. Therefore, the riser portion of the intake manifold of the engine flows in a liquid of emulsified state in the intake manifold and takes a substantial amount of time to reach the combustion chambers of the engine. For this reason, the fuel sucked into the intake manifold during cranking of the engine cannot be gasified rapidly with the result that the air/fuel mixture delivered to the combustion chambers of the engine cannot be enriched enough to significantly improve the cranking performance of the engine.
The present invention contemplates overcoming the above described drawback of a conventional spark-ignition internal combustion engine for automotive use.